Evaluation of three alum-precipitated Aeromonas hydrophila vaccines administered to Labeo rohita, Cirrhinus mrigala and Ctenopharyngodon idella: immunokinetics, immersion challenge and histopathology

Aeromonas hydrophila is a cause of infectious disease outbreaks in carp species cultured in South Asian countries including Pakistan. This bacterium has gained resistance to a wide range of antibiotics and robust preventive measures are necessary to control its spread. No prior use of fish vaccines has been reported in Pakistan. The present study aims to develop and evaluate inactivated vaccines against local strain of A. hydrophila in Pakistan with alum-precipitate as adjuvant. The immunogenic potential of vaccine was evaluated in two Indian major carps (Rohu: Labeo rohita, Mori: Cirrhinus mrigala) and a Chinese carp (Grass carp: Ctenopharyngodon idella). Fish were vaccinated intraperitoneally followed by a challenge through immersion. Fish with an average age of 4-5 months were randomly distributed in three vaccinated groups with three vaccine concentrations of 108, 109 and 1010 colony forming unit (CFU)/ml and a control group. Fixed dose of 0.1ml was applied to each fish on 1st day and a booster dose at 15 days post-vaccination (DPV). Blood samples were collected on 14, 28, 35, 48 and 60 DPV to determine antibody titers in blood serum using compliment fixation test (CFT). Fish were challenged at 60 DPV with infectious A. hydrophila with 108 CFU/ml through immersion. Significantly higher levels of antibody titers were observed from 28 DPV in all vaccinated groups as compared to those in the control group. In challenge experiment the average RPS (relative percent survivability) was 71% for groups vaccinated with 109 and 1010 CFU/ml and 86% for 108 CFU/ml. Vaccine with 108 CFU/ml induced highest immune response followed by 109 and 1010 CFU/ml. The immune response of L. rohita and C. idella was better than that of C. mrigala. In general, normal histopathology was observed in different organs of vaccinated fish whereas minor deteriorative changes were found in fish vaccinated with higher concentrations of the vaccine.

Dietary Vitamin A Improved the Flesh Quality of Grass Carp (Ctenopharyngodon idella) in Relation to the Enhanced Antioxidant Capacity through Nrf2/Keap 1a Signaling Pathway

Fish is an important animal-source food for humans. However, the oxidative stress-induced by intensive aquaculture usually causes deterioration of fish meat quality. The nutritional way has been considered to be a useful method for improving fish flesh quality. This study using the same growth experiment as our previous study was conducted to investigate whether vitamin A could improve flesh quality by enhancing antioxidative ability via Nrf2/Keap1 signaling in fish muscle. Six diets with different levels of vitamin A were fed to grass carp (Ctenopharyngodon idella) (262.02 ± 0.45 g) for 10 weeks. Dietary vitamin A significantly improved flesh sensory appeal and nutritional value, as evident by higher pH24h value, water-holding capacity, shear force, contents of protein, lipid, four indispensable amino acids (lysine, methionine, threonine, and arginine) and total polyunsaturated fatty acid in the muscle. Furthermore, dietary vitamin A reduced oxidative damage, as evident by decreased levels of muscle reactive oxygen species, malondialdehyde, and protein carbonyl, enhanced activities of antioxidative enzyme (catalase, copper/zinc superoxide dismutase (CuZnSOD), MnSOD, glutathione peroxidase, and glutathione reductase), as well as increased content of glutathione, which was probably in relation to the activation of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling. These findings demonstrated that dietary vitamin A improved flesh quality probably by enhancing antioxidant ability through Nrf2/Keap 1a signaling in fish.

Grass Carp (Ctenopharyngodon idella) KAT8 Inhibits IFN 1 Response Through Acetylating IRF3/IRF7

Post-translational modifications (PTMs), such as phosphorylation and ubiquitination, etc., have been reported to modulate the activities of IRF3 and IRF7. In this study, we found an acetyltransferase KAT8 in grass carp (CiKAT8, MW286472) that acetylated IRF3/IRF7 and then resulted in inhibition of IFN 1 response. CiKAT8 expression was up-regulated in the cells under poly I:C, B-DNA or Z-DNA stimulation as well as GCRV(strain 873) or SVCV infection. The acetyltransferase domain (MYST domain) of KAT8 promoted the acetylation of IRF3 and IRF7 through the direct interaction with them. So, the domain is essential for KAT8 function. Expectedly, KAT8 without MYST domain (KAT8-△264-487) was granularly aggregated in the nucleus and failed to down-regulate IFN 1 expression. Subcellular localization analysis showed that KAT8 protein was evenly distributed in the nucleus. In addition, we found that KAT8 inhibited the recruitment of IRF3 and IRF7 to ISRE response element. Taken together, our findings revealed that grass carp KAT8 blocked the activities of IRF3 and IRF7 by acetylating them, resulting in a low affinity interaction of ISRE response element with IRF3 and IRF7, and then inhibiting nucleic acids-induced innate immune response.

First Record of Pseudocapillaria tomentosa (Dujardin, 1845) Moravec, 1987 in Cultured Grass Carp in Basrah Province, Iraq

A total of 110 specimens of cultured grass carp Ctenopharyngodon idella (Pisces: Cyprinidae) were collected from three different fish pond stations in Basrah province, during the period from March till July 2007. Postmortem parasitological examinations indicated infection of the grass carp with the nematode Pseudocapillaria tomentosa and this infection occurred only in Faddak fish ponds during all months of investigation. The maximum incidence of infection was 26.6% in April, while the maximum intensity of infection was 8.5 in June. The present finding of this nematodes represents its first record in Iraqi fishes.